The present invention relates to an apparatus and thermoforming method for film on blister packing machines and, more specifically, to an apparatus and thermoforming method for film on blister packing machines, realized in such a way as to be capable of preventing warping of a blister sheet, when performing blister packaging by using a polypropylene film which is disposable by burning, and forming a film with a largest possible thickness at the portion of the film forming depressions (hereinafter referred to as xe2x80x9cpocketsxe2x80x9d).
Conventionally, in blister packaging for packaging tablets such as chemicals, etc. by using film such as PVC film, etc., the normal practice consists of heating a long film fed intermittently and continually as desired by pinching it between flat-shaped hot plates disposed face to face and movable in approaching and separating directions. In this heated and softened film, pockets are formed in which to house one or several pieces of tablets each by means of a forming die. The tablets are then fed into the respective pockets and the pockets are sealed by placing aluminum foil along the film having such pockets. The film is then cut so that the required number of pockets may be contained in one piece of sheet, as products.
The forming of film on the conventional blister packaging machines is generally made by unwinding film continuously or intermittently from a roll which took up PVC film in the shape of a tape. The entire face of the film is heated to a temperature suitable for forming pockets, by means of a heating unit, disposed in such a way as to face both faces of the film in linkage with the unwinding of the film, wherein the heating unit moves in approaching and separating directions against the film. The film is then fed to the forming system which forms part of the film into pockets of a required shape from a forming die disposed on one side of the forming system. After filling tablets into these pockets, the pockets are sealed by attaching aluminum foil thereto.
However, there was a problem that, while PVC film is suitable for forming part of a heated film into pockets of a required shape, the film thickness of the formed pockets, especially at the top face portion of the pockets, becomes extremely small compared with other parts of the film. This occurs because the pockets are formed by heating the entire face of the PVC film, and therefore, the pockets are easily deformed at the time of packaging the tablets, after filling the pockets with tablets, made by placing two sheets one upon another with their pockets facing each other and in opposite directions, or in the course of distribution or sale.
Moreover, when the PVC film in which pockets are formed is cut into sheets as blister sheets, the surrounding portion remaining after cutting in the shape of a sheet becomes scraps. The products and the scraps are taken out separately, and only the scraps are disposed of. However, the scraps, which produce a high temperature when burning that may damage an incinerator, have been disposed in landfills, etc. in recent years, thereby involving high scrap treating costs. To avoid this problem, the blister sheet has come to be formed by using polypropylene which can be burned in an ordinary refuse incinerator.
The polypropylene film sheet, like PVC film sheet, has a problem of becoming extremely thin at the formed pockets, especially at the position of the sheet forming the top face portion of the pockets, compared with other portions of the film, thereby making the pockets easily deformable after filling the pockets with tablets. Another problem is that, when the film is heated on the entire face when forming the pockets, the blister sheet after filling the pockets with tablets is warped because of a difference in coefficient of heat contraction between the polypropylene film sheet and the aluminum foil. This makes it impossible, when performing packaging of tablets by placing sheets one upon another with their pockets facing each other, to place the sheets one upon another automatically with a machine. Instead, the operation must be executed manually, thereby leading to poor working efficiency.
The objective of the present invention, realized in view of the problems produced when forming pockets by heating the film using the conventional blister packaging machine, is to provide an apparatus and thermoforming method for film on blister packing machines, realized in such a way as to form pockets without an extreme reduction in the thickness of the sheet at the top face portion of the pockets, and to enable sheets to be placed one upon another without warping.
To achieve this objective, the thermoforming method for film on blister packaging machines according to the present invention is characterized in that it consists of the pinching of a film, fed intermittently in synchronization with an open/close drive of the die on a thermoforming system, between the dies of the thermoforming system. Only the pocket forming portion of the film is locally heated by pressing the pocket forming portion into contact with the surface of hot plugs which face the pocket holes of the forming die. By injecting compressed air from a forming die side, stopping the injection of compressed air from the forming die side, and then injecting compressed air from a heating die side, the heated portion of the film is able to extend along the inner circumferential face of the pocket holes of the forming die to thereby form pockets.
This thermoforming method for film on blister packaging machines, realized in such a way as to heat only the pocket forming portion of the film locally and extend the heated portion of the film along the inner circumferential face of the pocket holes of the forming die to form pockets, is capable of forming blister sheets without warping, even when using polypropylene film, which is liable to be easily deformed due to thermal contraction because the portions of the film not forming pockets are not heated. The present invention is also capable of performing lap packaging of blister sheets by using an automatic machine and forming pockets without reducing the thickness of the sheet at the top face of the pockets, thus preventing deformation at the top face of the pockets after filling the pockets with tablets.
In this case, it may be so arranged that the plugs retreat when the heated portion of the film is extended along the inner circumferential face of the pocket holes of the forming die.
This makes it possible for the heated and softened film to separate accurately from the plugs of the heating die. The compressed air injected in this state acts uniformly on the film face, to accurately extend the heated portion of the film along the inner circumferential face of the pocket holes of the forming die and accurately form pockets.
Moreover, to achieve the same objective, the thermoforming system of film for blister packaging machines according to the present invention is a thermoforming system for film on blister packaging machines, realized in such a way as to pinch and heat the film, fed intermittently in synchronization with an open/close drive of the die on a thermoforming system, between the dies of the thermoforming system. The heated film is partially extended along the inner circumferential face of the pocket holes of a forming die to form pockets in the film. The dies of the thermoforming system are constructed with the forming die provided with pocket holes, and a heating die provided with plugs to locally heat only the pocket forming portion of the film disposed facing the pocket holes of the forming die. Injecting mechanisms which inject compressed air are disposed on the forming die side and the heating die side, respectively.
This thermoforming system for film on blister packaging machines, in which injecting mechanisms of compressed air on the forming die side and the heating die side are disposed respectively, is capable of heating only the pocket forming portion of the film locally and forming pockets by extending the heated portion of the film along the inner circumferential face of the pocket holes of the forming die. Therefore, blister sheets can be formed without warping, even when using polypropylene film which is liable to be easily deformed by thermal contraction, because the portions not formed into pockets are not heated. The thermoforming system according to the present invention can also perform lap packaging of blister sheets by using an automatic machine and form pockets without thickness reduction of the sheet at the top face of the pockets, thus preventing deformation at the top face of the pockets after filling the pockets with tablets.
The thermoforming system is constructed with a heating die and a forming die, so that the open/close operation of the heating die and forming die is performed in synchronization with the intermittent feeding of the film, and it is so arranged that the heated film is pressed by compressed air pressure in such a way as to lie along the pocket holes, thereby enabling the easy and accurate formation of pockets.
In this case, a compressed air injection hole may be formed at the inner bottom of the pocket holes of the forming die.
This makes it possible to heat the film by uniformly pressing it in contact with the plugs provided on the heating die from the forming die side, and form pockets of good accuracy in a beautiful shape.
Furthermore, it may be so arranged as to inject compressed air through the plug insertion holes in the heating die, and construct the heating die in the form of a water cooled jacket.
This makes it possible to clearly distinguish between the heated and non-heated heated portions of the film and form blister sheets without warping, because the non-heated portion is cooled even if the heated portion is heated to such an extent as to cause softening of the film.